The research objectives of this study are to continue a determination of the frequency of HBV transmission from women with acute hepatitis A and B during pregnancy and after the first 2 months of delivery and to continue to associate the relation of time of maternal infection to neonatal infection. Furthermore, we will continue to attempt to determine the frequency of HBV transmission from HBsAg carrier women to their newborn and such transmission by non-parenteral means later in life. An attempt to illuminate the mode of transmission from HBV infected mother to child by study of HBsAg, anti-HBs and, occasionally HBc, in the cord blood will be made. We will further the investigation of the natural course of HBV infection in infected infants with careful sequential, clinical, and laboratory studies. A continuation of the study of the duration of antigenemia in chronically HBV infected infants with serial determinations of HBsAg, anti-HBs, and occasionally HBc, will be made. We will sequentially test the family members of HBsAg carrier mothers to determine the frequency of non- parenteral HBV transmission from these women to members of the household and members of the community in general. An especially important aspect will be a periodic testing of the household contacts of all chronically infected HBV babies in our series to determine the frequency of non- parenteral transmission of this agent to siblings and other household members. This may well afford a unique opportunity in that it has been shown that HBsAg carriers who have signs of liver disease are more likely to be infectious to their contacts than carriers who are asymptomatic. Our infants and children have been shown to have chronic persistent hepatitis and are, therefore, prime suspects as a source of an HBV pool. Finally, we will enlarge upon our studies of hepatitis A by testing the stool of newborn infants of women who have type A hepatitis at delivery for the recently determined hepatitis A antigen.